In an internet protocol (IP) network, besides audio communication and data service, video distribution service requiring high-speed data transmission such as triple-play service in which broadcasting, telephone, and data communication are integrated is becoming active. Internet protocol television (IPTV) in triple-play service is one of the most important broadband applications.
A passive optical network (PON) system provides high-speed broadband Internet access using an optical fiber network to user terminals placed in individual households. The PON system is composed of plural optical network units (ONUs) each placed in a user's home and accommodating at least one user terminal and an optical line terminating apparatus (OLT) connected to these ONUs through an optical fiber network.
The optical fiber network of the PON system is composed of a trunk optical fiber connected to the OLT, plural branch optical fibers connected to the ONUs, and an optical splitter (or optical coupler) for joining the branch optical fibers and the trunk optical fiber, and takes the form of an optical distribution network (ODN) in which the plurality of ONUs can share the optical transmission line between the OLT and the optical splitter.
In the PON system, the cost of laying optical fibers can be greatly reduced compared to other broadband access technologies. Particularly in a G-PON (Gigabit-Capable PON) system, variable-length data frames can be transmitted at gigabit high speed, which can offer various broadband network applications to end users. Details of G-PON are disclosed in ITU-T G.984.1 “Gigabit-capable Passive Optical Networks (GPON): General characteristics”, ITU-T G.984.2 “Gigabit-capable Passive Optical Networks (GPON): Physical Media Dependent (PMD) layer specification”, and ITU-T G.984.3 “Gigabit-capable Passive Optical Networks (GPON): Transmission convergence layer specification.”